Apparatus for determining fluid flow

ABSTRACT

The present invention is an apparatus for determining the flow rate of a fluid in a pipe. The apparatus includes a device for providing acoustic energy on a diagonal path through the fluid. The diagonal providing device is in contact with the pipe. The apparatus also includes a device for providing acoustic energy on a diametrical path through the fluid. The diametrical providing device is in contact with the pipe. The apparatus is also comprised of a device for determining the flow of fluid in the pipe based on the acoustic energy of the diagonal providing device with the energy received by the diameterical receiving means used to determine the speed of sound of the fluid so the flow rate of fluid can be determined and the acoustic energy of the diametrical providing device. In one embodiment, the diagonal providing device is fixedly disposed on the pipe. In another embodiment, the diametrical providing device provides acoustic energy emitted in both directions on the diametrical path. The diagonal providing device preferably includes a first transducer and a second transducer located at diametrically opposed positions about the pipe. The first transducer and second transducer are preferably adapted to alternatively function as transmitter and receiver so as to cause ultrasonic signals to travel through the fluid along the diametric path. The diametrical providing device preferably includes a third transducer and a fourth transducer located at diagonally opposed upstream and downstream positions relative to one another.

This is a continuation of application Ser. No. 07/957,411 filed on Oct.6, 1992, now abandoned.

FIELD OF THE INVENTION

The present invention relates in general to flowmeters. Morespecifically, the present invention is related to flowmeters usingultrasonic transducers for the noninvasive measurement of attributes ofa fluid, such as its flow, in a pipe.

BACKGROUND OF THE INVENTION

A convenient and commonly used means of measuring fluid flow is by theuse of ultrasonic flowmeters. This is typically accomplished by a systemin which two transducers, located at angularly opposed upstream anddownstream positions relative to one another are adapted toalternatively function as a transmitter and a receiver thereby causingultrasonic signals to travel alternatively in upstream and downstreamdirections between the transducers. The difference in transit timesbetween the upstream signal and the downstream signal can be used tocalculate the flow rate of the fluid.

The present invention in a preferred embodiment provides a second set oftransducers which are disposed in a diametrical opposed relation. These"cross path" transducers provide more information about the flow field,allowing for improvement in flow measurement accuracy and understandingof the flow field.

SUMMARY OF THE INVENTION

The present invention is an apparatus for determining the flow rate of afluid in a pipe. The apparatus includes means for providing acousticenergy on a diagonal path through the fluid. The diagonal providingmeans is in contact with the pipe. The apparatus also includes means forproviding acoustic energy on a diametrical path through the fluid. Thediametrical providing means is in contact with the pipe. The apparatusis also comprised of means for determining the flow of fluid in the pipebased on the acoustic energy of the diagonal providing means and theacoustic energy of the diametrical providing means with the energyreceived by the diametrical receiving means used to determine the speedof sound of the fluid so the flow rate of fluid can be determined.

In one embodiment, the diagonal providing means is fixedly disposed onthe pipe. In another embodiment, the diametrical providing meansprovides acoustic energy emitted in both directions on the diametricalpath. The diametrical providing means preferably includes a firsttransducer and a second transducer located at diametrically opposedpositions about the pipe. The first transducer and second transducer arepreferably adapted to alternatively function as transmitter and receiverso as to cause ultrasonic signals to travel through the fluidalternatively along the diametric path.

The diagonal providing means preferably includes a third transducer anda fourth transducer located at diagonally opposed upstream anddownstream positions relative to one another. The third transducer andthe forth transducer are preferably adapted to alternatively function asa transmitter and receiver so as to cause ultrasonic signals to travelthrough the fluid in upstream and downstream directions along thediagonal path between the third transducer and the fourth transducer.The diametric path is adjacent to the diagonal path so that thetransducers are sampling the same portion of fluid.

The determining means preferably comprises signal processing means fordetermining the flow of fluid in the pipe based on the transmissionspeed of ultrasonic signals transmitted between the first and secondtransducers and the third and fourth transducers.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, the preferred embodiment of the inventionand preferred methods of practicing the invention are illustrated inwhich:

FIG. 1 is a schematic representation showing an apparatus fordetermining fluid flow in a pipe.

FIG. 2 is a schematic representation showing the geometric parametersassociated with the apparatus for determining fluid flow in a pipe.

FIG. 3 is a schematic representation showing the signal processing meansof the apparatus for determining fluid flow in a pipe.

FIG. 4 is a schematic representation of the apparatus for determiningfluid flow in a pipe having a four ultrasound paths.

FIG. 5 is a schematic representation showing an apparatus fordetermining fluid flow in a pipe using a bounce path.

FIG. 6 is a schematic representation of an apparatus for determiningfluid flow using transducers disposed below the pipe's surface.

FIG. 7 is a schematic representation showing an apparatus fordetermining the axial transverse velocity profile.

FIG. 8 is a schematic representation of an apparatus for determiningfluid flow in a pipe using three transducers.

FIG. 9 is an image of a transverse velocity profile of a pipe.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein like reference numerals refer tosimilar or identical parts throughout the several views, and morespecifically to FIGS. 1 and 2 thereof, there is shown an apparatus 10for determining the flow rate of a fluid 11 in a pipe 12. The apparatus10 comprises means for providing acoustic energy on a diagonal path 18through the fluid 11. The diagonal providing means is in acousticcontact with and preferably disposed on the pipe 12. The apparatus 10also comprises means for providing acoustic energy on a diametrical path24 through the fluid 11. The diametrical providing means is in acousticcontact with and preferably disposed on the pipe 12. The apparatus 10 isalso comprised of means for determining the flow of fluid 11 in the pipe12 based on the acoustic energy of the diagonal providing means and theacoustic energy of the diametrical providing means. In one embodiment,the diagonal providing means is fixedly disposed on the pipe 12. Inanother embodiment, the diametrical providing means provides acousticenergy emitted in both directions on the diametrical path 24.

Referring to FIG. 1, the diametrical providing means is preferablycomprised of a first transducer 14 and a second transducer 16 located atdiametrically opposed upstream and downstream positions relative to oneanother. The first transducer 14 and second transducer 16 are preferablyadapted to alternatively function as transmitter and receiver so as tocause ultrasonic signals to travel through the fluid 11 alternatively inupstream and downstream directions along a diametric path 18 between thefirst transducer 14 and the second transducer 16.

The diagonal providing means is preferably a third transducer 20 and afourth transducer 22 located at diagonally opposed positions about thepipe 12. The third transducer 20 and the forth transducer 22 arepreferably adapted to alternatively function as a transmitter andreceiver so as to cause ultrasonic signals to travel through the fluid11 along a diagonal path 24. The diametric path 18 is adjacent to thediagonal path 24 so that the transducers are essentially sampling thesame portion of fluid 11.

The determining means preferably comprises signal processing means 26for determining the flow of fluid 11 in the pipe 12 based on thetransmission speed of ultrasonic signals transmitted between the firstand second transducers 14, 16 and the third and fourth transducers 20,22, respectively.

Preferably, the transducers 14, 16, 20 and 22 are mounted on the outsideof the pipe 12 and thus do not disturb the fluid flow therein. Thecoupling between the third and fourth transducers 20, 22 and the pipe 12is preferably accomplished by mounting the third and fourth transducers20, 22 onto a coupling wedge 28 which can be comprised of vespal orlucite, for example. The first and second transducers 14, 16 are mountedon a pad 30, which can also be comprised of vespal or lucite. Thecoupling between the wedges 28 and pads 30 and the pipe 12 can beenhanced by providing a layer 32, such as silicon rubber. The layer 32helps in preventing disruption or dispersion of the ultrasonic signalsas they travel from their respective wedge 28 or pad 30 to the pipe 12.Preferably, the signal processing means 26 includes means for measuringthe transit time of ultrasonic signals transmitted between the first andsecond transducers 14, 16 and the transit time between ultrasonic signaltransmitted between the third and fourth transducers 20, 22,respectively.

In a preferred embodiment, there is a plurality of diagonal sets oftransducers for transmitting ultrasonic signals through the fluid 11along a plurality of diagonal paths 24 and an equal number ofdiametrical sets of transducers for transmitting ultrasonic signalthrough the fluid 11 along a plurality of diametrical paths 18. FIG. 4shows a cross section through the axis of the pipe 12 showing a fourpath system. Since FIG. 4 is a cross sectional view, the transducersshown can be either diagonal sets or diametrical sets. Likewise, thefour paths shown can be either diagonal paths 18 or diametrical paths24.

It should be noted that in FIG. 2 and the specification, the followingnomenclature is used:

Q=total flow in pipe 12 (cubic inches/sec)

II=Pi=3.141593

ID=Inside diameter of pipe 12 (inches)

PF=Hydraulic profile factor=ratio of average velocity over whole pipe 12to average velocity along diameter

c.sub.ƒ =velocity of sound in fluid 11 (inches/sec)

φ.sub.ƒ =angle of acoustic path in fluid 11

t_(d1) =transit time along diagonal path 18 from transducer 14 totransducer 16

t_(d2) =transit time along diagonal path 18 from transducer 16 totransducer 14

Δt_(d) =difference in time along diagonal path 18 (seconds) that isΔt_(d) =t_(d1) -t_(d2)

t_(c1) is transit from transducer 20 to transducer 22

t_(c2) is transit from cross path transducer 22 to transducer 20

Δt_(c) =difference in time along diametrical cross path 24 (seconds)that is Δt_(c) =t_(c1) -t_(c2)

c_(w) =velocity of sound in transducer wedge 28 and pad 30 (inches/sec)

φ=mechanical wedge 28 angle

a_(w) =height of wedge (inches)

a_(wc) =height of pad 30

a_(p) =wall thickness of pipe 12 (inches)

φ_(p) =acoustic path angle in pipe 12

φ_(w) =acoustic path angle in wedge 28

c_(pt) =velocity of transverse wave in pipe 12 (inches/sec)

c_(pl) =velocity of longitudinal wave in pipe 12 (inches/sec)

t_(d) =average transit time along diagonal path 18 (seconds) that ist_(d) =(t_(d1) +t_(d2))/2

t_(c) =average transit time along diametrical path 18 (seconds) that ist_(c) =(t_(c1) =t_(c2))/2

y is the distance between centers of transducers 14, 16

y_(o) is the calculated value of y to be used in initial set uptemp=Temperature in degrees F

press=Pressure in psi absolute

press=pressure gauge+14.7

tr, vt, dvdp, tc are parameters used in the calculation of velocity ofsound in water

Acpl, Bcpl, Acpt, Bcpt are constants used in calculation of velocity ofsound in pipe (dependent on pipe material)

Acw, Bcw, Ccw are constants used in calculation of velocity of sound inwedge (dependent on wedge material)

The flow rate Q of the fluid is calculated by:

    Q=(π·ID.sup.2 ·PF/4)·v.sub.a

since,

    v.sub.a =v.sub.d /Sinφ.sub.ƒ -v.sub.c /Tanφ.sub.ƒ

and,

    v.sub.d =(c.sub.ƒ.sup.2 ·Cosφ.sub.ƒ /2·ID)·(Δt.sub.d)

    v.sub.c =(c.sub.ƒ.sup.2 /2·ID)·(Δt.sub.c) (0)

Thus,

    v.sub.a =(c.sub.ƒ.sup.2 /2·ID·Tanφ.sub.ƒ)·(Δt.sub.d -Δt.sub.c)

substituting into the original equation,

    Q=(π·ID·PF·C.sub.ƒ.sup.2 /8·tanφ.sub.ƒ)·(Δt.sub.d -Δt.sub.c)                                          (1)

For acoustic path-to-transmitter length ratios less than 16:1, φ.sub.ƒis calculated using Snells law relationship as follows:

    φ.sub.ƒ =sin.sup.-1 (c.sub.ƒ sinφ.sub.w /c.sub.w)

For acoustic path-to-transmitter length ratios greater than 100:1,calculation of φ.sub.ƒ is given by solution of the followingsimultaneous equations:

    t.sub.d =2·a.sub.w /Cosφ.sub.w ·c.sub.w +2·a.sub.p /Cosφ.sub.p ·c.sub.pt +ID/Cosφ.sub.ƒ ·c.sub.ƒ    (2)

    Sinφ.sub.ƒ /c.sub.ƒ =Sinφ.sub.p /c.sub.pt (Snells law)                                                      (3)

    Sinφ.sub.ƒ /c.sub.ƒ =Sinφ.sub.w /c.sub.w (Snells law)                                                      (4)

Ideally, the acoustic path-to-transmitter length ratio should be chosento fall clearly into one of these regions. Alternatively, if this cannotbe achieved, then the fourth transducer is moved axially along the pipe12 until the position is found at which the signal transferred from thethird transducer 20 to the fourth transducer 22 is a maximum. At thispoint, either set of the above equations can be used.

If y is known φ.sub.ƒ is given by solution of the following set ofequations:

    y=2·a.sub.w ·Tanφ.sub.w +2·a.sub.p ·Tanφ.sub.p +ID·Tanφ.sub.ƒ

    Sinφ.sub.ƒ /c.sub.ƒ =Sinφ.sub.p /c.sub.pt Snells law

and

    Sinφ.sub.ƒ /c.sub.ƒ =Sinφ.sub.w /c.sub.w Snells law

Calculation of y_(o)

    Sinφ.sub.ƒ =c.sub.ƒ ·Sinφ.sub.wo /c.sub.w Snells law

    Sinφ.sub.p =c.sub.pt ·Sinφ.sub.wo /c.sub.w Snells law

    y.sub.o =2·a.sub.w ·Tanφ.sub.w +2·a.sub.p ·Tanφ.sub.p +ID·Tanφ.sub.ƒ

Calculation of c.sub.ƒ is given by solution of equation:

    t.sub.c =ID/c.sub.ƒ +2·a.sub.p /c.sub.pl +2·a.sub.wc /c.sub.w                             (5)

The speed of sound values are dependent on temperature. t_(c) ismeasured with the first transducer 14 and the second transducer 16through the diametric path 18 therebetween. C_(pt), C_(pi) and C_(w) aredetermined by the following equations.

    c.sub.pt =Acpt*(1+Bcpt*temp)                               (6)

    c.sub.pl =Acpl*(1+Bcpl*temp)                               (7)

    c.sub.w =Acw*(1+Bcw*temp+Ccw*temp 2)                       (8)

ID, a_(p) and a_(wc) are known (measured) from the specific applicationof the apparatus.

With c.sub.ƒ known by solution of Equation (5), t_(d) measured with thethird transducer 20 and the fourth transducer 22 through the diagonalpath 24 therebetween, and a_(w), c_(w) and a_(p), c_(pt) and ID known,solution of, for example, the three Equations (2)-(4) determine thethree unknowns φ_(w), φ_(p) and φ.sub.ƒ in these equations.Consequently, Q can then be determined since every variable in Equation(1) is now known.

For instance, for carbon steel pipe 12

Acpl=2356000

Bcpl=0.0000735

Acpt=127700

Bcpt=0.0000925

For vespal wedges 28

Acw=98299

Bcw=0.0003960

Ccw=2.08E-7

To calculate c.sub.ƒ in water temperatures>200° F.

    tr=temp-175.1                                              (9)

    vt=5290.52-0.15302*tr-0.0138265*tr 2+3.326E-6 *tr 3+3.11042*tr 4-5.1131E-11*tr 5                                         (10)

    dvdp=756.78/(725-temp)+6.3846-0.034241*(725-temp) +7.4075-5*(725-temp) 2-5.666E-8*(725-temp) 3                                   (11)

    vtp=vt-(4437-press)*dvdp*0.02253                           (12)

    c.sub.ƒ =vtp*12                                   (13)

To calculate c.sub.ƒ at water temperatures<200° F. ##EQU1##

The above equations assume that the wedges 28, pipe 12 and fluid 11 areall at the same temperature. When the temperature of the fluid 11 isdifferent from that of ambient temperature, it is desirable to provideinsulation or other means to insure that the temperature is uniform orto modify the equations given above to correct for these differences.For small gradients it is sufficient to assign different temperatures tothe wedges and pipe thus

temp(pipe)=temp(fluid)-Δt_(p)

temp(wedge)=temp(fluid)-Δt_(w)

temp(cross wedge)=temp(fluid)-Δt_(wc)

where

Δt_(w) is the difference between the fluid temperature and the averagetemperature of the wedge

Δt_(wc) is the difference between the fluid temperature and the averagetemperature of the cross wedge or pad

Δt_(p) is the difference between the fluid temperature and the averagetemperature of the pipe

For large gradients, it is desirable to have detailed knowledge of thetemperature distribution in the pipe and wedge and to use ray tracingtechniques as practiced in the design of optical instruments tocalculate the times spent in the wedge and pipe and contribution of thepipe and wedge to the y displacement.

If the temperature of the fluid is not known, as shown in the "REMCalculation of Fluid Temperature" section of the program of theAppendix, c.sub.ƒ as well as the temperature of the water can be arrivedat in an iterative loop technique that essentially picks a temperaturevalue of the water based on the known temperature limits of the water,uses this temperature value to arrive at values of c.sub.ƒ c_(wc) andc_(pl), and then uses the values of c.sub.ƒ, c_(wc) and c_(pl) inequation (5) to arrive at a calculated value of t_(c). The actualmeasured value of t_(c) is then compared with the calculated value oft_(c).

If the calculated value of t_(c) does not match the measured value oft_(c), different temperature values are sequentially picked in theprogram and the loop is reiterated until the calculated value of t_(c)matches the measured value of t_(c). The picked temperature and thecalculated value of c.sub.ƒ during the last loop are then known to bethe actual values of temperature and c.sub.ƒ.

In this manner, both the speed of sound in the fluid, c.sub.ƒ, and thetemperature of the fluid 11 flowing in the pipe 12 can be determined bymounting a pair of ultrasonic transducers in a diametrical opposedrelation on the pipe 12 and using signal processing means to determine ameasured value of t_(c).

In the operation of the invention, the transducers 14, 16, 20 and 22 arepreferably strap-on types. The strap-on transducer assembly contains apiezoelectric transducer, a coupling wedge 28 or pad 30 and a protectivecover. The transducer converts the electrical energy to ultrasonicenergy which the wedge 28 and pads 30 directs into the pipe 12 at theproper angle. The protective cover provides a fitting for the transducercable 36 conduit as well as protection of the transducer.

After precisely locating the transducer on the surface of the pipe 12,the transducer wedge is coupled acoustically to the pipe wall and thensecured with strapping material, magnetic holders, or welded brackets.

The transducer signal cable is a twinax twisted pair with a shield withan appropriate jacket for underwater or above ground use as required. Itis connected to the transducer at one end and to the signal processingmeans 26 at the other, normally without splices.

The signal processing means 26 is comprised of three major functionalunits. These are the Acoustic Processing Unit 100 (APU), the CentralProcessing Unit 102 (CPU), and the Control and Display Panel 104 (CDP).FIG. 3 provides a functional diagram of these electronics.

The APU 100 controls the transmission and reception of ultrasonicsignals to and from the transducers. Electronic pulses are generated andsent to the transducers, where the energy is converted into ultrasoundand directed upstream or downstream in directly into the pipe dependingon which transducer is transmitting , converted back into electronicpulses, and received. Transmit times of pulses are measured with a 100Mhz clock, alternately upstream and downstream, every 4 ms to assurethat data is essentially simultaneous for upstream and downstreamtransit times. These time measurements are stored and then sent to thecentral processing unit 102 for mathematical manipulation.

The APU 100 typically is equipped with two transmitter/receiver boardswhich control a total of four ultrasonic diagonal paths 18.Additionally, there are two transmitter/receiver boards to control fourultrasonic diametric paths 24.

The CPU 102 consists of a 286 microprocessor and I/O with softwaresuited specifically to the needs of the application. The CPU 102provides a number of important functions, including processing thetransit time measurements from the APU 100. Flow totalizers are alsoupdated according to Euler's equation. At the same time as high speedcalculations are being processed, the displays are updated, electronicchecks are being made of the entire APU 100 circuitry, user keypadcommands are followed, and outputs are updated.

The CDP 104 functions as the user interface. A full screen display 106provides readouts of flowrates, flow totals, diagnostics, set-upparameters, and pertinent performance characteristics. A numeric keypad108 allows the operator to select desired display screens withoutconsulting a programmer's handbook and without need of attaching aseparate computer.

Listed below in Tables 1 through 3 are summaries of the calculatedparameters for two verification sites. These verification sites were theAlden Research Laboratories (ARL) and the Tennessee Valley Authority(TVA) Sequoyah Nuclear Power Plant. The ARL test used a 16 in OD pipewith fluid temperature at approximately 105° Fahrenheit. (The datapresented below are documented by ARL which is an NIST approvedfacility). The TVA test used a 32 in OD pipe with fluid temperature atapproximately 435° Fahrenheit. Independent error analysis determined itsaccuracy to be ±0.9% of measured flow.

                  TABLE 1                                                         ______________________________________                                        Flow Calculation at ARL 12/18/91                                              ______________________________________                                        Conditions:                                                                   ID             =     15.028 in (Direct Measurement)                           pressure       =     50 psi                                                   a.sub.p        =     .495 in (Direct Measurement)                             temp           =     105.32° (ARL Reference)                           Q              =     18,390 gpm (ARL Reference)                               c.sub.w        =     92,170 in/sec (Direct                                                         Measurement)                                             φ.sub.wo   =     30.550                                                   c.sub.pl       =     233,774 in/sec (Curve fit from                                                Published values)                                        a.sub.wc       =     .25 in                                                   c.sub.pt       =     125,454 in/sec (Curve fit from                                                Published values)                                        a.sub.w        =     .586 in                                                  LEFM Measured values:                                                         t.sub.d1       =     291.86 μsec                                           t.sub.d2       =     290.66 μsec                                           t.sub.d1       =     241.45 μsec                                           t.sub.c2       =     241.45 μsec                                           Δt.sub.d =     1218 ns                                                  t.sub.c        =     241.45 μsec                                           Δt.sub.c =     -4 ns                                                    t.sub.d        =     291.26 μsec                                           LEFM Calculated values:                                                       c.sub.f        =     60,260 in/sec                                            temp           =     105°                                              Q              =     18,488 gpm                                               φ.sub.f    =     19.4°                                             φ.sub.w    =     30.53°                                            φ.sub.p    =     43.75°                                            y              =     6.92 in                                                  y.sub.o (calculated)                                                                         =     6.92 in                                                  ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Flow Calculation at ARL 12/18/91                                              ______________________________________                                        Conditions:                                                                   ID             =     15.028 in (Direct Measurement)                           a.sub.p        =     .495 in (Direct Measurement)                             temp           =     105.19° (ARL Reference)                           Q              =     13,430 gpm (ARL Reference)                               c.sub.w        =     92,170 in/sec (Direct                                                         Measurement)                                             c.sub.pl       =     233,774 in/sec (Curve fit from                                                Published values)                                        c.sub.pt       =     125,454 in/sec (Curve fit from                                                Published values)                                        LEFM Measured values:                                                         t.sub.d        =     291.26 μsec                                           t.sub.c        =     241.45 μsec                                           Δt.sub.d =     890 ns                                                   Δt.sub.c =     -3 ns                                                    LEFM Calculated values:                                                       c.sub.f        =     60,260 in/sec                                            temp           =     105°                                              Q              =     13,480 gpm                                               φ.sub.f    =     19.4°                                             ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Flow Calculation at TVA Sequoyah 2/6/92                                       ______________________________________                                        Conditions:                                                                   ID             =     29.92 in (Indirect Measurement)                          a.sub.p        =     1.194 in (Direct Measurement)                            temp           =     428° (TVA RTD Measurement)                        c.sub.w        =     82,750 in/sec (Direct                                                         Measurement and Curve Fit)                               c.sub.pl       =     223,466 in/sec (Curve fit from                                                Published values)                                        c.sub.pt       =     124,322 in/sec (Curve fit from                                                Published values)                                        LEFM Measured values:                                                         t.sub.d        =     670.32 μsec                                           t.sub.c        =     612.22 μsec                                           Δt.sub.d =     1413 ns                                                  Δt.sub.c =     1 ns                                                     LEFM Calculated values:                                                       c.sub.f        =     50,386 in/sec                                            temp           =     428.8°                                            Q              =     13.518 Mlbs/hr                                           φ.sub.f    =     19.4°                                             ______________________________________                                    

In an alternative embodiment, as shown in FIG. 5, the third transducer20 and the fourth transducer 22 are aligned with each other such thatacoustic energy transmitted by the third transducer 20 follows adiagonal path to the fourth transducer 22 which is formed by reflectionof the acoustic energy off of the pipe 12. This configuration of theapparatus 10, as shown in FIG. 5, is otherwise known as the bounce pathconfiguration. The first transducer 14 and the second transducer 16which create the diametrical path 18, are disposed adjacent the diagonalpath 24 that forms the bounce path, either between the third transducer20 and fourth transducer 22 or outside the third transducer 20 or fourthtransducer 22. The equations described above are also applicable todetermine flow in the bounce path configuration of FIG. 5. An example ofsuch a configuration is the following:

Q=472 gpm

ID=27.25 inches

PF=1.00

c.sub.ƒ =47,275.7 inches

φ_(p) =18.35°

t_(d1) =385.180 μsec

t_(d2) =385.000 μsec

Δt_(d) =180 nsec

t_(c1) =179.008 μsec

t_(c2) =179.000 μsec

Δt_(c) =8 nsec

c_(w) =92,046.09 inches/sec

φ_(wo) =38.52°

a_(w) =0.642 inches

a_(wc) =0.250 inches

a_(p) =0.360 inches

φ_(p) =57.74°

φ_(w) =37.80°

c_(pt) =126,989.7 inches/sec

c_(pl) =231,992.8

t_(d) =385.090 μsec

t_(c) =179,004 μsec

y=7.5

y_(o) =7.423

temp=74° F.

pressure=775 psi

Conditions

Pipe ID=7.9529 inches

a_(p) =0.3605 inches

temp=74°

c_(pl) =231,945.8 in/sec (from tables)

c_(pt) =126,956.3 in/sec (from tables)

c_(w) =91,987.1 (direct measurement)

LEFM Measurements

t_(d) =386 μsec

t_(c) =180 μsec

Δt_(d) =177 nsec

Δt_(c) =8 nsec

LEFM Calculated Values

c.sub.ƒ =47,001.3 in/sec. (φ_(w) =37.18°)

Q=468 gpm (φ_(p) =56.51°)

φ.sub.ƒ =17.98°

In another alternative embodiment, as shown in FIG. 6, the pipe 12 hasan outside surface 27 and an interior 29 and the first transducer 14 andsecond transducer 16 are disposed in the pipe 12 beneath the outsidesurface 27 such that acoustic energy transmitted by the first transducer14 is introduced into the interior 29 of the pipe 12, an acoustic energyis received by the second transducer 16 directly from the interior 29 ofthe pipe 12 as shown in FIG. 6. The diametrical path 18 is thus formedwithout having acoustic energy, preferably ultrasonic energy, passingdirectly through the pipe 12. Preferably, the third transducer 20 andfourth transducer 22 are disposed in the pipe 12 beneath the outsidesurface 27 such that acoustic energy transmitted by the third transducer20 is introduced directly into the interior 29 of the pipe, and acousticenergy is received by the fourth transducer 22 directly from theinterior 29 of the pipe 12 after it has taken a diagonal path 24therethrough. Of course, the third transducer 20 and fourth transducer22 can be mounted on the outside 27 of the pipe 12 as described above,or, the various transducers can be mounted on or below the outsidesurface 27 depending on the design choice such that only one transducer,three transducers, etc. can be on or below the outside surface 27. Thealgorithm associated with calculation of the flow and other relevantfactors for the embodiment shown in FIG. 6 can be found in Caldontechnical report DS-112-991 (incorporated by reference) with respect toa single pair of transducers forming a diagonal ultrasonic path. For thepair of transducers forming the diametrical ultrasonic path θ=90°, Cosθ=1 yielding the transverse flow velocity V. For a 4-path configuration,see Caldon technical report DS-116-392 (incorporated by reference). Theplacement of the transducers beneath the outside surface 27 of the pipe12 is well known. See Caldon technical report installation procedureSP1041 Rev. C, incorporated by reference.

The present invention also pertains to an apparatus for creating atransverse velocity profile of fluid flowing in a pipe 12. The apparatuscomprises means for obtaining a transverse velocity of fluid in aplurality of different locations in the pipe 12 by introducing energyinto the pipe 12 and analyzing the energy. Preferably, the obtainingmeans includes means for providing acoustic energy along a plurality ofdiametrical paths in the pipe 12, all of which are in a common crosssection of the pipe 12, and producing an information signalcorresponding to the transverse velocity of the plurality of differentlocations. The providing means can be a plurality of transducers whichcreate a plurality of diametrical paths 18 in the pipe 12 as shown inFIG. 4. Each diametrical path 18 identifies the transverse velocitycomponent associated with a corresponding location in the pipe 12. Thetransverse velocity corresponding to each diametrical path 18 can bedetermined by Equation (0).

The apparatus is also comprised of means for forming a transversevelocity profile from the transverse velocities at the plurality ofdifferent locations. The forming means is in communication with theobtaining means. Preferably, the forming means includes signalprocessing means 26. The signal processing means 26 receives theinformation signal and determines the transverse velocity associatedwith each location. Each pair of transducers which form a diametricalpath 18 can be connected to signal processing means 26 as describedabove to calculate the transverse velocity for the correspondingdiametrical path 18. Preferably, the more diametrical paths 18 in agiven cross section of the pipe, the more accurate the transversevelocity flow profile will be.

Preferably, the forming means includes a monitor in which the transversevelocity of the locations are displayed together to show the transversevelocity profile. An example of a display that would appear on a monitoris shown in FIG. 9 which shows the rotational component both in theclockwise and counterclockwise direction cross section of the pipe 12. Aratio of V_(c) :V_(D) can be used to deduce the flow profilecharacteristic (see Weske, J. "Experimental Investigation of VelocityDistributions Downstream of Single Duct Bends," NACA-TN-1471, January,1948, incorporated by reference). The flow profile characteristic can beused to choose path(s) with the lowest diametrical to diagonal velocityratio.

The present invention also pertains to an apparatus for determiningtransverse velocity of fluid in a pipe 12. The apparatus is comprised ofmeans for actively testing the flowing fluid with energy and producing atest signal corresponding to the transverse velocity of the fluid. Thetesting means is in contact with the pipe 12. The apparatus 106 is alsocomprised of signal processing means 26 for determining the transversevelocity of the fluid based on the test signal. The signal processingmeans 26 is in communication with the transverse velocity testing means106. As described above, the testing means is preferably a firsttransducer 14 and a second transducer 16 which are in contact with thepipe 12 such that they form a diametrical path 18. From Equation (0),the transverse velocity can be obtained with the signal processing means108.

The present invention also pertains to a method for creating a velocityprofile of fluid flowing through an axial length 110 of pipe 12 as shownin FIG. 7. The method comprises the steps of (a) measuring transversevelocity flow of the fluid at a first axial location 112 of the pipe 12with energy introduced therein. Then, there is the step of (b) measuringtransverse velocity flow of the fluid at a second axial location 114 ofthe pipe 12 with energy introduced therein. Preferably, after step (b),there is the step (c) of forming a profile of the transverse velocity offluid flowing in the pipe 12 over the axial length 110 of the pipe fromthe transverse velocity measured at the first axial location 112 andsecond axial location 114. Preferably, before step (c), there is thestep (d) of measuring the transverse velocity of fluid flowing in thepipe 12 at a plurality of additional different axial locations, such asaxial location 116 with energy introduced to the pipe 12. After the step(d), there can be the step (e) of fixing a flow meter in contact withthe pipe 12 at a desired axial location based on the transverse velocityflow thereat.

Also as shown in FIG. 7, there is an apparatus 118 for creating avelocity profile of fluid flowing through a pipe 12. The apparatus 118is comprised of means 120 for obtaining transverse velocity flowinformation of fluid along an axial length 110 of the pipe 12 withenergy introduced therein. The apparatus 118 is also comprised of means122 for forming a transverse velocity profile along the axial length 110of the pipe 12 from the transverse flow information. The forming means122 is in communication with the obtaining means 120. Preferably, theobtaining means 120 can be a plurality of transducers 124 disposed in aremovable housing, for instance, connected with velcro. The transducers124 are disposed in the housing 126 such that each transducer 124 has amate transducer 124, which together form a diametrical path. Individualsets of transducers provide their diametrical path information to theobtaining means 122, which is preferably signal processing means 26 asdescribed above, to calculate the transverse flow. The forming means 122can also include a monitor 121 which is connected to signal processingmeans 26 that displays the velocity profile along the axial length 110.A flow meter, for instance, comprised of first transducer 14, secondtransducer 16, third transducer 20 and fourth transducer 22, as shown inFIG. 1, can then be fixedly attached to the pipe 12 at a location wherethere is minimal transverse velocity flow so that an accurate a readingas possible of the axial flow through the pipe 12 can be obtained.

The present invention is also an apparatus for measuring the temperatureof a flowing fluid 11 in a pipe 12. The apparatus is comprised of meansfor actively testing the flowing fluid with energy and producing a testsignal corresponding to the temperature of the fluid 11. The testingmeans is in contact with and preferably disposed on the outside of thepipe 12. The apparatus is also comprised of signal processing means 26for determining the temperature of the fluid 11 based on the testsignal.

Preferably, the testing means comprises a first transducer 14 fortransmitting ultrasonic signals through the fluid 11 and a secondtransducer 16 for receiving ultrasonic signals transmitted by the firsttransducer 14. The second transducer 16 is disposed in an opposingrelation with the first transducer 14 such that the ultrasonic signalstransmitted by the first transducer 14 travel on a diametric path 18with respect to the pipe 12 to the second transducer 16. Preferably, thetesting means also includes means for measuring pressure of the fluid inthe pipe 12, such as a pressure gauge or sensor. The pressure measuringmeans is in communication with the signal processing means 26 and thepipe 12. The signal processing means 53 preferably determines thetemperature of the fluid in the pipe 12 based on the transmission speedof ultrasonic signals transmitted between the first and secondtransducers and the pressure of the fluid. Preferably, the signalprocessing means 26 identifies the average temperature of the fluidacross the pipe 12 corresponding to the diametric path 18 between thefirst transducer 14 and second transducer 16. Preferably, to calculatethe temperature, Equations 9-14 below can be used in the signalprocessing means 20, such as a computer. By being disposed on theoutside of the pipe 12, the first and second transducers do notinterfere with the flow of fluid 11 with the pipe. The temperature ofthe fluid 11 flowing in the pipe 12 can thus be determined without theapparatus penetrating the envelope defined by the inside diameter, ID,of the pipe 12.

The present invention is also an apparatus for measuring the speed ofsound in a fluid 11 flowing in a pipe 12. The apparatus comprises meansfor testing the flowing fluid 11 and producing a test signalcorresponding to the speed of sound of the fluid in the pipe. Thetesting means is in contact with and preferably disposed on the outsideof the pipe 12. The apparatus also includes signal processing means 26for determining the speed of sound of the fluid in the pipe based on thetest signal. Preferably, the testing means is disposed in a gaseousenvironment on the outside of the pipe 12. Preferably, the testing meanscomprises a first transducer 14 for transmitting ultrasonic signalsthrough the fluid 11 and a second transducer 16 for receiving ultrasonicsignals transmitted by the first transducer 14. The second transducer 16is disposed in an opposing relation with the first transducer 14 suchthat the ultrasonic signals transmitted by the first transducer 14travel on a diametric path 18 with respect to the pipe 12 to the secondtransducer 16. The speed of sound can be determined by the signalprocessing means 26, such as a computer, with Equations (5), (7) and (8)and the necessary measured data.

The present invention also pertains to an apparatus 10 forcharacterizing fluid properties in a pipe 12. The apparatus 10 comprisesfirst means for measuring sound velocity in the fluid and producing afirst signal corresponding to the sound velocity. The first measuringmeans is in communication with the fluid. The apparatus 10 is alsocomprised of second means for measuring at least one state variable ofthe fluid and providing a second signal corresponding to the statevariable measured. The second means is in communication with the fluidin the pipe. Additionally, the apparatus is comprised of signalprocessing means 26 in communication with the first and second measuringmeans for determining fluid properties. As shown in FIG. 1, the secondmeasuring means preferably includes means for measuring pressure of thefluid. The pressure measuring means is connected with the signalprocessing means 26. The pressure measuring means can be a pressuresensor in communication with the fluid. The first means can include afirst transducer 14 and a second transducer 16 in contact with the pipesuch that first transducer 14 transmits acoustic energy in a diametricpath 24 to the second transducer 16. Each transducer is in communicationwith the signal processing means 26.

In this embodiment, preferably, the signal processing means 26 alsodetermines specific volume of the fluid. The specific volume can bedetermined from the "REM calculation" as specific volume cubicfeet/pound" in Appendix A. For this calculation, the pressure isindependently measured with a pressure gauge and the temperature iscalculated from the speed of sound, as described above. Additionally,the signal processing means 24 can determine Reynolds number for thefluid in the pipe from the specific volume and viscosity andconsequently PF. It does this in the following way. The determination ofthe kinematic viscosity (kvis), the profile factor PF and the Reynoldsnumber can be obtained from "REM calculation of meter factor" inAppendix A, where L represents log. The profile correction factor, PF,relates to axial velocity averaged along the acoustic path between thediagonal transducers, v, with the axial velocity average across thecross sectional area of the flow, v. This is expressed as: ##EQU2##

The PF will vary depending on three factors. These are:

(1) Average fluid velocity, v.

(2) Fluid density and viscosity, ρ and μ, respectively.

(3) Cross section dimensions (i.e. ID).

The Reynolds number combines the hydraulic effect of the above 3 factorsinto one number. The Reynolds number, Re, can be used to determine anexpression for the velocity profile (Nikuradse, J. "Laws of TurbulentFlow in Smooth Pipes," NASA TT F-10, 359, October, 1966; Reichardt, H.,"Vollstandige Darstellung der turbelenten Geskhwindigkeitsverteilung inglatten Leitungen" ZAMM 31, 208-219 (1951), incorporated by reference)and thus the PF may be determined from knowledge of the Reynolds number.

The LEFM first calculates the kinematic viscosity using the curve fit ofthe published values for water vs. temperature.

where:

υ=Kinematic viscosity=μ/υ=absolute viscosity/density

Then, the Reynolds number is calculated:

Re=Reynolds number=Dv/υ

The PF is then calculated using published data (i.e. Reichardt andNikuradse) that express the velocity profile as a function of Reynoldsnumber.

In the apparatus 10, with temperature measuring means, the signalprocessing means 24 preferably identifies when a boundary between fluidof a first material and fluid of a second material passes through thepipe at the diametrical path. The temperature measuring means can be,for instance, a thermal couple in contact with the pipe 12 or the fluid.Since there is independent identification of temperature and pressure,and with an essentially constant temperature and pressure, a change inspecific volume determined by the first and second transducers andsignal processing means 26 indicates a change in material in the pipe12. Knowledge of the pressure, temperature and sound velocity can beused to distinguish fluids which have sound velocities distinct fromeach other. Typically, fluid with sound velocities that differ by 0.5%at a given temperature and pressure are easily distinguished. Likewise,with knowledge of the pressure and calculated temperature, the specificheat content of water and water density can be determined from a curvefit of published data vs. temperature and pressure. Fluid enthalpy canbe determined using the fluid density and specific heat content.

Another embodiment requires only three transducers to form a diagonaland a diametrical path, as shown in FIG. 8. Second transducer 16 andfourth transducer 22 are the same as described above. In place of firsttransducer 14 and third transducer 20 is double transducer 23. On afirst face 25 forming a 45° angle with the surface 27 is disposedpiezoelectric 37 which emits ultrasonic energy. The ultrasonic energy isincident upon the double transducer 23-pipe 12 interface where a portionof the energy is refracted therethrough ultimately to third transducer22, and a portion of the energy is reflected to free face 33. Free face33 forms a 22.5° angle with the outer surface 27 of the pipe 12. Thereflected energy from the double transducer 23-pipe 12 interface isagain reflected by free face 33 such that it forms a right angle withthe outer surface of the pipe 12 and is transmitted therethrough tosecond transducer 16.

Although the invention has been described in detail in the foregoingembodiments for the purpose of illustration, it is to be understood thatsuch detail is solely for that purpose and that variations can be madetherein by those skilled in the art without departing from the spiritand scope of the invention except as it may be described by thefollowing claims.

    __________________________________________________________________________        : REM High Temperature Strapon Flowmeter method 1                         pi = 3.141593  'value of Pi                                                   rad = 180 / pi  'conversion from radians to degrees                           REM measured pipe and wedge dimensions                                        awc = .247'wedge height cross path, inches                                    aw = .7825'wedge height diagonal wedge , inches                               Thetawo = 30.55 / rad                                                         OD = 16.04' Pipe diameter inches                                              ap = .992 'Pipe wall thickness, inches                                        ID = OD - 2 * ap' calculation of pipe inside diameter                         tauEc = (2.64 + 1.075) * .000001'Tau electronics + Tau transducer + Tau       cab                                                                           cross path, seconds                                                           tauEd = (1.64 + 1.075) * .000001'Tau electronics + Tau transducer + Tau       cab                                                                           diagonal path, seconds                                                        pressg = 1100' measured fluid pressure                                        press = pressg + 14.7'conversion from press gauge to press absolute           REM measured values of times                                                    td = .0003387' average transit time diagonal path, seconds                    tc = .00029542#' average transit time cross path, seconds                     dtd = 7.59E-07'difference in transit time diagonal path, seconds              dtc = -1E-09'difference in transit time cross path, seconds                 REM Coefficients used in calculation of velocity of sound in pipe and         wedge                                                                           Acw = 98299: bcw = -.000396054#: ccw = -2.08E-07'KKB Vespal corrected       ??                                                                              Acpt = 127700: Bcpt = -.0000925                                               Acpl = 235600: Bcpl = -.0000735                                             REM coefficients for calculation of lkvis= natural log kvis                     Akv = -5.507787: Bkv = -.01557479#: Ckv = 2.87701E-05: Dkv                  = -1.8516E-08                                                                 REM calculation of fluid temperature                                            Th = 660: Tl = 165: 'temperature limits                                       dto = .001 ' max error in calculation of temp                                 dt = Th - Tl                                                                DO                                                                              i = i + 1                                                                     dt = dt / 2                                                                   temp = Tl + dt                                                                cwc = Acw * (1 + bcw * tempwc + ccw * tempwc   2)  ' velocity in wedge,     inches                                                                        /sec                                                                            cpl = Acpl * (1 + Bcpl * tempp)'longitudinal velocity in steel,             inches/sec                                                                      tr = temp - 175.1                                                             vt = 5290.52 - .15302 * tr - .0138265 * tr   2 + 3.326E-06 * tr   3 +       3.11042                                                                       -08 * tr  4 - 5.1131E-11 * tr   5                                               dvdp = 756.78 (725 - temp) + 6.3846 - .034241 * (725 - temp)                + 7.407E-05 * (                                                               725 - temp)   2 - 5.666E-08 * (725 - temp)   3                                  vtp = vt - (4437 - press) * dvdp * .02253                                     cf = vtp * 12                                                                 tau1 = tauEc + 2 * awc / cwc + 2 * ap / cpl'Tau for cross path                F1 = tc - tau1 - ID / cf                                                      IF F1 >= 0 THEN Tl = temp                                                   LOOP UNTIL ABS(dt) < dto OR F1 = 0                                            REM calculation of Tangent phif                                               sphiw = SIN(Thetawo)' Sine of wedge angle                                     cw = Acw * (1 + bcw * temp + ccw * temp   2) ' velocity of sound in           wedge,i                                                                       s/sec                                                                         sphif = cf * sphiw / cw' Sine of angle on fluid                               cphif = SQR(1 - sphif   2)' Cosine of angle in fluid                          tphif = sphif / cphif' Tangent of angle in fluid                              REM calculation of meter factor                                                 v = cf   2 / 2 / ID / tphif * (dtd - dtc)                                     Lkvis = Akv + Bkv * temp + Ckv * temp   2 + Dkv * temp   3 'natural log     kine                                                                          tic viscosity of water, square inches/sec                                       lre = LOG(ABS(v * ID)) - Lkvis 'Calculation of natural log Reynold's        number                                                                          PF = 1.0144 - .8442 / lre  'meter factor                                    REM calculation of flow                                                       Q = pi * ID * PF * cf   2 / (8 * tphif) * (dtd - dtc)' flow in cubic          inches/sec                                                                    PRINT Q                                                                       END                                                                             REM calculation os specific volume cubic feet/pound                            svt = .01566 + 6.97E-06 * temp - 6.27E-08 * temp   2 + 3.61E-10 * temp       3 - 7.34E-13 * temp   4 +0 5.5E-16 * temp  5                                   dsvdp = 70931 / (700 - temp) - 17.9 + .01621 * (700 - temp) + .000004      * (700 - temp)   2                                                               svtp = svt + (3000 - press) * dsvdp * 1E-08                                __________________________________________________________________________

What is claimed is:
 1. An apparatus for determining fluid flow rate in apipe comprising:a first transducer for transmitting acoustic energy,said first transducer in acoustic contact with said pipe; a secondtransducer for receiving said acoustic energy from said firsttransducer, said second transducer in contact with said pipe such thatthe acoustic energy transmitted by the first transducer follows asubstantially diametrical path through the fluid in the pipe; a thirdtransducer for transmitting acoustic energy, said third transducer inacoustic contact with said pipe; a fourth transducer for receiving saidacoustic energy transmitted from said third transducer, said fourthtransducer in acoustic contact with said pipe such that the acousticenergy transmitted by said third transducer follows a diagonal paththrough the fluid in the pipe, said diametrical path adjacent to saiddiagonal path; wherein each transducer is disposed on the outside of thepipe and acoustic energy follows a path through the pipe wall, andsignal processing means for determining the flow rate of fluid in thepipe based on acoustic energy received by the second and fourthtransducers with the energy received by the second transducer used todetermine the speed of sound of the fluid so the flow of fluid can bedetermined, said second and fourth transducers in communication withsaid signal processing means.
 2. An apparatus as described in claim 1wherein the third transducer and fourth transducer are located atupstream and downstream positions relative to one another, said thirdand fourth transducers adapted to alternatively function as transmitterand receiver so as to cause acoustic signals to travel through the fluidalternatively in upstream and downstream directions along a diagonalpath between the third transducer and the fourth transducer; and whereinthe first and second transducers are adapted to alternatively functionas transmitter and receiver so as to cause acoustic signals to travelthrough the fluid alternatively between said first and secondtransducers along a diametrical path, said diametrical path adjacent tosaid diagonal path; and wherein the signal processing means includesmeans for determining the flow rate of fluid in the pipe based on thetransmission speed of acoustic signals transmitted between the first andsecond transducers and the third and fourth transducers, respectively.3. An apparatus as described in claim 2 wherein the pipe has an outsidesurface and the first, second, third, fourth transducers are fixed tothe outside surface of the pipe.
 4. An apparatus as described in claim 3including a plurality of sets of transducers for alternatelytransmitting and receiving acoustic signals through the fluid along aplurality of diagonal paths.
 5. An apparatus as described in claim 4including a plurality of sets of transducers for alternatelytransmitting and receiving acoustic energy through the fluid along aplurality of diametrical paths.
 6. An apparatus as described in claim 1wherein the third transducer and the fourth transducer are aligned witheach other such that acoustic energy transmitted by the third transducerfollows a diagonal path to the fourth transducer which is formed byreflection of the acoustic energy off of the pipe.
 7. An apparatus asdescribed in claim 1 wherein the pipe has an outside surface and aninterior and the third and fourth transducers are disposed in the pipebeneath the outside surface such that acoustic energy transmitted by thethird transducer is introduced directly into the interior of the pipe,and acoustic energy is received by the fourth transducer directly fromthe interior of the pipe.
 8. An apparatus for determining fluid flowrate in a pipe comprising:means for providing acoustic energy on adiagonal path through the fluid, said diagonal providing means fixedlydisposed on said pipe; means for receiving said acoustic energy on thediagonal path, said diagonal receiving means disposed on said pipe;means for providing acoustic energy on a diametrical path through thefluid, said diametrical providing means disposed on said pipe; means forreceiving said acoustic energy on the diametrical path, said diametricalreceiving means disposed on said pipe; wherein each providing means andreceiving means is disposed on the outside of the pipe and acousticenergy follows a path through the pipe wall, and means for determiningthe flow rate of fluid in the pipe based on the acoustic energy receivedby the diagonal receiving means and the acoustic energy received by thediametrical receiving means with the energy received by the diametricalreceiving means used to determine the speed of sound of the fluid so theflow rate of fluid can be determined, said determining means incommunication with the diagonal providing means and the diagonalreceiving means, and the diametric providing means and the diametricreceiving means.
 9. An apparatus as described in claim 8 wherein thediagonal providing means and diagonal receiving means comprises a thirdtransducer and a fourth transducer, respectively, located on the pipe atupstream and downstream positions relative to one another and thediametric providing means and diametric receiving means comprises afirst transducer and a second transducer, respectively, located on thepipe at opposed diametric positions relative to one another.
 10. Anapparatus as described in claim 9 wherein said third and fourthtransducers adapted to alternatively function as transmitter andreceiver so as to cause acoustic signals to travel through the fluidalternatively in upstream and downstream directions along the diagonalpath between the third and fourth transducers and said first and secondtransducers adapted to alternatively function as transmitter andreceiver so as to cause acoustic signals to travel through the fluidalternatively along the diametrical path between said first and secondtransducers.
 11. An apparatus as described in claim 10 wherein the meansfor determining flow rate includes signal processing means.
 12. Anapparatus as described in claim 11 wherein the signal processing meansincludes means for determining the flow rate of fluid in the pipe basedon the transmission speed of acoustic signals transmitted between thefirst and second transducers and the third and fourth transducers,respectively.
 13. An apparatus as described in claim 12 including aplurality of sets of transducers for alternately transmitting andreceiving acoustic signals through the fluid along a plurality ofdiagonal paths.
 14. An apparatus as described in claim 13 including aplurality of sets of transducers for alternately transmitting andreceiving acoustic energy through the fluid along a plurality ofdiametrical paths.
 15. An apparatus for determining fluid flow rate in apipe comprising:means for providing acoustic energy on a diagonal paththrough the fluid, said diagonal providing means in contact with saidpipe; means for providing acoustic energy on a diametrical path throughthe fluid, said diametrical providing means in contact with said pipe;means for receiving said acoustic energy on the diagonal path; means forreceiving said acoustic energy on the diametrical path; wherein eachsaid providing mean and each said receiving means is disposed on theoutside of the pipe and acoustic energy follows a path through the pipewall to said providing and said receiving means, and means fordetermining the flow rate of fluid in the pipe based on the acousticenergy of the diagonal providing means and the acoustic energy of thediametrical providing means, said determining means in communicationwith the diagonal providing means and the diametric providing means. 16.An apparatus as described in claim 15 wherein the diagonal providingmeans comprises a third transducer and a fourth transducer located onthe pipe at upstream and downstream positions relative to one anotherand first and second transducers located on the pipe at opposeddiametric positions relative to one another.
 17. An apparatus asdescribed in claim 16 wherein said third and fourth transducers adaptedto alternatively function as transmitter and receiver so as to causeacoustic signals to travel through the fluid alternatively in upstreamand downstream directions along the diagonal path between the third andfourth transducers and said first and second transducers adapted toalternatively function as transmitter and receiver so as to causeacoustic signals to travel through the fluid alternatively along thediametrical path between said first and second transducers.
 18. Anapparatus as described in claim 17 wherein the means for determiningflow rate includes signal processing means.
 19. An apparatus asdescribed in claim 18 wherein the signal processing means includes meansfor determining the flow rate of fluid in the pipe based on travel timeof acoustic signals transmitted between the first and secondtransducers, and the third and fourth transducers, respectively.
 20. Anapparatus for determining fluid flow in a pipe comprising:a firsttransducer for transmitting acoustic energy, said first transducer inacoustic contact with said pipe; a second transducer for receiving saidacoustic energy from said first transducer, said second transducer incontact with said pipe such that the acoustic energy transmitted by thefirst transducer follows a substantially diametrical path through thefluid in the pipe; wherein each transducer is disposed on the outside ofthe pipe and acoustic energy follows a path through the pipe wall, and athird transducer for transmitting acoustic energy, said third transducerin acoustic contact with said pipe; a fourth transducer for receivingsaid acoustic energy transmitted from said third transducer, said fourthtransducer in acoustic contact with said pipe such that the acousticenergy transmitted by said third transducer follows a diagonal paththrough the fluid in the pipe, said diametrical path adjacent to saiddiagonal path, wherein the third transducer and fourth transducer arelocated at upstream and downstream positions relative to one another,said third and fourth transducers are adapted to alternatively functionas transmitter and receiver so as to cause acoustic signals to travelthrough the fluid alternatively in upstream and downstream directionsalong a diagonal path between the third transducer and the fourthtransducer; and wherein the first and second transducers are adapted toalternatively function as transmitter and receiver so as to causeacoustic signals to travel through the fluid alternatively between saidfirst and second transducers along the diametrical path, saiddiametrical path adjacent to said diagonal path; and signal processingmeans for determining the flow of fluid in the pipe based on acousticenergy received by the second and fourth transducers, said second andfourth transducers in communication with said signal processing meanswherein the signal processing means includes means for determining theflow rate of fluid in the pipe based on how long it takes of acousticsignals transmitted between the first and second transducers and thethird and fourth transducers, respectively.
 21. An apparatus fordetermining fluid flow in a pipe comprising:means for providing acousticenergy on a diagonal path through the fluid, said diagonal providingmeans fixedly disposed on said pipe, the diagonal providing meanscomprises a third transducer and a fourth transducer located on the pipeat upstream and downstream positions relative to one another; means forproviding acoustic energy on a diametrical path through the fluid, saiddiametrical providing means disposed on said pipe, the diametricalproviding means comprises a first transducer and a second transducerlocated on the pipe at opposed diametric positions relative to oneanother; wherein each said providing means and said receiving means isdisposed on the outside of the pipe and acoustic energy follows a paththrough the pipe wall, and means for determining the flow of fluid inthe pipe based on the acoustic energy of the diagonal providing meansand the acoustic energy of the diametrical providing means, saiddetermining means in communication with the diagonal providing means andthe diametric providing means.